Tanks may be designed in many different configurations, such as spheres, cylinders, cones and shells in general, as well as prismatic shapes. The principal advantage of prismatic shapes is that they nest closer to each other, minimising the volume taken up by such tanks. Simple prismatic tanks are far less efficient structurally as they rely on bending action for mobilisation of strength. Shells develop strength through direct tension in the plane of the shell. This develops greater strength for the same amount of material.
A more efficient design of prismatic shapes is to incorporate internal stays (tension beams) and frames to absorb unbalanced loads. By developing stays as the main means of restraining the internal load or pressure augmented by web frames to absorb un-symmetric load components such as due to acceleration of the tank contents, such prismatic stayed tanks are comparable to shell shapes in structural efficiency. WO 2006/001711 A2 discloses such tanks and is hereby incorporated by reference.
Apart from developing structural strength the stays and the web frames dampen sloshing induced by wave motion. The horizontal loads on the tension stays and web frames due to sloshing are absorbed by the beams and the webs.
Certain metal structures have welded connections which develop lower strength than the base metal. This in particular applies to certain alloys which also are suitable for cryogenic applications. Web frames or walls sustaining loads applied out of their central plane sustain peak bending at supports in the form of intersecting frames or walls. A more effective design is to make the welded connections away from the support and as close as possible to points of inflection where stress is lower. Placing such low strength welds away from areas of high stress is also desirable for reasons of safety. Such low strength welds may cause very local yielding causing premature rupture with little deformation in the event of excessive thermal stress or other accidental load. This is particularly critical in the case cryogenic and combustible cargoes.